1. Field of the Invention
The present invention relates to a surface acoustic wave device adapted for a high frequency electronic device, and particularly, to a surface acoustic wave device that has its preferred performance adapted for use in the field of a land mobile radio telephone systems or portable radio telephone systems and can be manufactured by simplified bonding processes to improve reliability and is suitable for mass production.
2. Description of the Related Art
A surface acoustic wave device, such as a surface acoustic wave filter, is a three terminal or four terminal type element that has an electrode for inputting and is outputting and formed of Al and so forth on a piezoelectric substrate having a large electromechanical coupling coefficient and a relatively small temperature coefficient in the frequency, such as 36.degree. Y-X LiTaO.sub.3 monocrystalline substrate.
There are many interdigital electrodes (also called comb electrodes) having teeth, (i.e., the width (L) of the electrode strip and the interval (S) of the electrode strip), and the pitch (P) of the electrode strip, in a design of normally L=S=.lambda./4, P=.lambda./2 assuming that the. wavelength of the surface wave is .lambda.. For example, in order to obtain 836 MHz of center frequency, .lambda.=4.8 .mu.m is derived from the acoustic velocity 4090 m/s of .times.propagating surface wave under the interdigital electrode on the substrate. Thus, the pitch of the electrodes becomes 2.4 .mu.m and the width and interval of the electrodes becomes 1.2 .mu.m.
Typical devices have a pair of comb electrodes for input and output opposing each other. However, in a certain fields of use, such as in the field of mobile radio telephones, portable radio telephone and so forth, surface acoustic wave filters having a low amplitude attenuation (for example, less than or equal to 3 to 5 dB of insertion loss) and high suppression (for example, 24 to 25 dB of attenuation magnitude out of a pass band) in a wide range (for example, wider than or equal to 25 MHz of pass band at a center frequency higher than or equal to 836 MHz).
Various methods have been proposed in order to satisfy the foregoing performance. As one of the typical methods, there is the surface acoustic wave filter having a multi-electrode construction (see M. Lewis, 1982 Ultrasonic Symposium proceedings, P12, for example).
FIG. 1 shows an electrode pattern in the conventional surface acoustic wave device, which illustrates the surface acoustic wave filter with multi-electrode construction (example of 5 inputs-4 outputs). In the drawing, 1' denotes a device element, such that the comb electrodes 15 constituted of input and output electrodes arranged alternatively on 36.degree. Y-X LiTaO.sub.3 monocrystalline piezoelectric substrate. The device element is thus of a multi-electrode construction having five stages at the input side and four stages at the output side. The signal side electrode terminals are connected to an input terminal pad 11'a and output terminal pad 11'b which are, in turn, connected to external circuits. Although it is not illustrated, reflectors may be provided at both sides for improving the characteristics.
The reference numeral 11'c denotes grounding electrode strip pads formed electrically independent of each other.
The reference numeral 111' denotes a metal pattern for shielding formed surrounding the periphery of the element except for the input and output terminal pads 11'a and 11'b.
These comb electrodes, such as terminal pad and metal pattern and so forth, are typically formed simultaneously in photo-lithographic technology by deposition of the same metal, such as Al or Al-Cu alloy. It should be noted that the illustrated comb electrode is of a so-called normal type-normal construction that has an equal overlapping length of comb electrode strips. Width and number of the electrode strips on the drawing should not be considered accurate and are illustrated for simplification of the drawing.
FIGS. 2A and 2B show an example of practical installation of the conventional surface acoustic wave device. In the drawing, the reference numeral 1' denotes the above-mentioned device element in multi-pole construction. The reference numeral 2' denotes a package that comprises a ceramic box type container formed with a metallic wiring pattern 21' on the intermediate portion of the inner wall, for example (normally, this metallic wiring pattern is formed in a pattern corresponding to that of the terminal pads of the device element 1', and is connected to a not shown external terminal of the package). In the practical installation of the element, after die bonding the device element 1' onto the bottom of the package 2', connection is established between the input terminal pad 11'a and the output terminal pad 11'b (including the grounding metal pattern 111' for shielding if necessary) of the device element 1' and the metallic wiring pattern 21' by means of wires 7. Finally, the metallic lid plate 20' is sealed and fitted to complete the surface acoustic wave device, such as the multi-electrode construction of the surface acoustic wave filter.
However, in the above-mentioned conventional surface acoustic wave device, a space for wire bonding is required in the package. Particularly, in the multi-electrode construction of the device, there are many terminal pads and accordingly an increased number of wire bondings is required. Therefore the amount of required space increases. Furthermore, as a result of the enhancement in the working frequency range of the device to be used, the size of the comb electrodes and the terminal pads becomes smaller. Thus, the making of a junction by wire bonding becomes more difficult. Also, checking the quality of bonding becomes difficult. Furthermore, a problem arises in that the miniaturization of the surface acoustic wave device is frustrated due to large size of the package in proportion to the size of the device element.
The above-mentioned problems can be solve by a surface acoustic wave device housing a surface acoustic wave device element 1 which includes an electrode 15 formed on a piezoelectric substrate 10 in a package 2. The surface acoustic wave device comprises a metal bump 11 being formed on a bonding pad section of the surface acoustic wave device element 1, and the metal bump 11 being contact connected with a metal pattern 21 of the package 2. Practically, the metal pattern 21 may be formed on a lid plate 20 or bottom plate 22 of the package 2, or, as an alternative, a plurality of metal bumps 11 for grounding may be contact connected with the metal pattern 21. Also, a grounding bump pattern 111 may be formed along the periphery of the surface of the surface acoustic wave device element 1, on which the electrode is arranged. Alternatively, the surface acoustic wave device element 1 formed of the grounding bump pattern 111 may be contact connected with the metal pattern, and the whole element may be coated with a resin. Furthermore, a recess 200 or projection 201 for positioning of the surface acoustic wave device element 1 is provided on the metal pattern 21.
According to the present invention, since the metal bump 11 is provided on the terminal pad of the surface acoustic wave device element 1, it is not necessary to perform wire bonding at packaging and thus facilitate installation of the element. Particularly, this is effective for the multi-electrode construction type and can provide a higher reliability.
Also, since it is not necessary to provide a space for wire bonding in the package 2, the device can be made compact. Furthermore, it is simple to perform testing of the connection of the signal lines and grounding lines by means of a tester, and can improve isolation between an input and an output by providing the grounding metal pattern 21c.